Shemiras Halashon Halachos

Hilchos Rechilus, chapter 5, section 3

However, if one sees from the beginning of the story that listening to it may save him from bodily or financial harm, one may listen to the story and suspect it may be true as in hilchos lashon hara (p. 56). But the Torah forbids believing the story. To see how to behave optimally, see above hilchos lashon hara (p. 58). 29) If one sees clear signs that a person wants to cause him physical or financial harm even if one has heard nothing of it from anyone, one can investigate the matter with people in order to defend oneself. One need not be concerned that this is causing people to denigrate him.

Hilchos Rechilus, chapter 5, section 4

30. Even if one saw no clear signs of such a thing but only surprising behavior that slightly indicate that something is happening, one may investigate. One should not absolutely believe what one hears. The degree of suspicion is according to all the rules explained in hilchos lashon hara (p 61). One may not speak against or cause any harm to the person because every Jew is presumed to be kosher. Nor may one exempt oneself from money one owes to him even if one would be exempt from paying him according to what one heard. One may also not hate him, and must do kindness to him as with any Jew.